Phobos was a Soviet mission to Mars consisting of 2 nearly identical spacecraft. The mission included cooperation from 14 other nations including Sweden, Switzerland, Austria, France, West Germany, and the United States (who contributed the use of its Deep Space Network for tracking the twin spacecraft). The objectives of the dual mission were to 1) conduct studies of the interplanetary environment, 2) perform observations of the Sun, 3) characterize the plasma environment in the Martian vicinity, 4) conduct surface and atmospheric studies of Mars, and 5) study the surface composition of the Martian satellite Phobos. In support of these objectives, the mission was to perform the first close scientific investigation of and landing on another planet's moon. In addition to their on-board instrument complement, each vehicle carried a lander designed to land on Phobos' surface and perform a number of in-situ measurements. Phobos 2 also carried a second, smaller "hopper" lander designed to land on Phobos and then use its spring loaded legs to move ("hop") about the moon's surface to make chemical, magnetic and gravity observations at different locations. Phobos 1 operated nominally until controllers lost contact with the spacecraft on September 2, 1988 following a routine software upload (before the vehicle entered Mars orbit). Post-failure analysis traced the problem to an erroneous software command that had deactivated the attitude control thrusters, which resulted in the spacecraft
orienting the solar arrays away from the Sun, depleting the batteries. Phobos 2 operated
nominally throughout its cruise and Mars orbital insertion phases, gathering data on the Sun, interplanetary medium, Mars, and Phobos. Phobos 2 entered Mars orbit on January 29, 1989. Contact with the vehicle was lost on March 27, 1989 shortly before the final phase of the mission during which the spacecraft was to approach within 50 meters of Phobos' surface and release its two landers. The cause of the failure was determined to be a malfunction of the on-board computer.